The influence of the hypothalamic releasing factors CRF and GRF on the hormonal secretion of pituitary adenomas has been determined in vitro and correlated with patients' response in vivo. These studies indicate that the pituitary tumors causing Cushing's disease, Nelson's Syndrome and acromegaly are responsive to their appropriate releasing factor. We are also investigating the influence of the releasing facdors on the rate of growth of pituitary tumors in vitro. By understanding the mechanism of the secretory responses of these tumors to the releasing factors, new therapeutic methods may evolve.